The present invention relates to a method and device for controlling the power consumption of a mobile radio device, and in particular a mobile phone, having a pulse width modulation DC/DC-converter for converting a battery supply voltage to an internal supply voltage for an internal electrical circuit of said mobile radio device.
Although applicable to any mobile radio devices, the present invention and its underlying problems will be discussed with particular reference to GSM mobile systems.
In present generations of mobile phones, DC/DC-converters are often used to generate an internal supply voltage for an associated internal electrical circuit, such as a digital part formed as an integrated circuit, in order to achieve the lowest possible current consumption, thus keeping the battery operation time as long as possible. This is especially beneficial, if the internal supply voltage is low compared to the battery supply voltage, i.e. in case of a DC/DC-downconverter.
FIG. 4 shows a simplified block diagram of a usual mobile phone having a pulse width modulation DC/DC-converter for converting a battery supply voltage to an internal supply voltage of a baseband digital part.
In FIG. 4 reference sign B denotes a battery, R1 a first voltage regulator, R2 a second voltage regulator, R3 a third voltage regulator, 10 a baseband digital part, 20 a baseband analog part, 30 a radio frequency part, 40 a transmitter, 50 an antenna, 60 a loudspeaker, and 70 a microphone.
The first voltage regulator R1 is pulse width modulation DC/DC-downconverter for downconverting a battery supply voltage to an internal supply voltage of the baseband digital part 10 which part is usually supplied with the lowest voltage present in the phone.
The second voltage regulator R2 for the baseband analog part 20 and the third voltage regulator R3 for the radio frequency 30 are linear regulators because of the low noise requirements of the analog circuits in the baseband analog part 20 and the radio frequency part 30, respectively.
The technical problem associated with the concept of the mobile phone shown in FIG. 4 is the large dynamic range of the load current for the baseband digital part 10 to be supplied by the first voltage regulator R1 in form of said pulse width modulation DC/DC-downconverter.
A typical situation is indicated in FIG. 5 which,shows the load current of the baseband digital part 10 as a function of time for a GSM mobile phone in the standby state (a similar profile may be found in other mobile phone systems).
From FIG. 5 it can be seen that the power is drawn in very short load bursts of approximately 2 ms, typically spaced 0.5-2 s apart. The start of the bursts xcexcP-on corresponds to the microprocessor starting its activity associated with the sychronization of the network and paging procedures which lead to a current consumption of the order of 20-50 mA. Once the microprocessor stops its activity, the digital baseband part 10 goes to sleep mode and the current drops very low to a value of the order of 200 xcexcA as only a simple counter is running at a 32,768 kHz oscillator for counting up to the time of the next activity period.
With the demand of decreasing size of the mobile phones, also the components L and C of the pulse width modulation DC/DC-converter should be made physically minimized, i.e. their capacitance and inductance values be made lower. However, decreased capacitance and inductance values require an increased switching frequency in order to keep the output power constant.
On the other hand, a high switching frequency results in higher losses in the DC/DC-converter, leading to a lower power efficiency, especially at low loads.
FIG. 6 shows the efficiency loss of a typical DC/DC-converter as a function of the load current between 0 and 50 mA, and FIG. 7 as a function of the load current between 1 and 5 mA.
In FIGS. 6 and 7, lq denotes the quiescent current losses mainly originating from and being proportional to the bias currents of the comparator and error amplifier, lf the switching losses being proportional to the frequency, and lr the I2R losses for a parasitic output resistance R.
As becomes readily apparent from FIGS. 6 and 7, the quiescent current losses lq and the switching losses lf dominate at low output currents, i.e. in the sleep mode, while the I2R losses lr become comparable at high output currents, i.e. in the activity mode.
Today, various schemes are used to overcome this problem. Some of the most popular are often referred to as PFM (pulse frequency modulation), fixed on-time or fixed off-time. According to these schemes, the switching frequency is changed according to the load. This is achieved either by measuring the output current and adjusting the switching frequency accordingly (PFM), or by using a comparator which measures the output voltage to control the switch.
Both methods require increased circuit complexity compared to a fixed frequency PWM converter and both have decreased load regulation performance at low switching frequencies. The comparator controlled type furthermore involves a larger output ripple inherent to the nature of this control scheme.
The present invention provides a method and device for controlling the power consumption of a mobile radio device, and in particular a mobile phone, having a pulse width modulation DC/DC-converter for converting a battery supply voltage to an internal supply voltage, as defined in independent claims 1 and 6, respectively.
The principal idea underlying the present invention is to use information available in the mobile radio device to change the operating mode of the DC/DC-converter in order to save power, thus improving the operation time of the device. The changeover of the operating mode from sleep mode to an active mode is controlled by an internal logical control signal. It is this control signal which according to the invention is also used to switch the DC/DC-converter from a low power requirement mode having a low PWM frequency to a high power requirement mode having a high PWM frequency, namely not as a reaction of a changing load current, but anticipating a changing load current.
A particular advantage is that the load regulation problem described above is eliminated. Furthermore, the circuit complexity is low, because existing information is used, thus preventing the need for load current sensing circuitry.
The mobile radio device, i.e. the mobile phone, has increased performance due to the fact that the efficiency of the DC/DC-converter can always be kept at optimum.
Preferred embodiments of the present invention are listed in the respective dependent claims.
According to a preferred embodiment, said at least one switchable component for said pulse width modulation DC/DC-converter is selected from among the group of: a switchable oscillator having at least two switchable frequencies, a comparator having a switchable bias current source having at least two switchable comparator bias currents, an error amplifier having a switchable bias current source having at least two switchable error amplifier bias currents, and a switchable error amplifier reference voltage source having at least two switchable error amplifier reference voltages. These are the essential power determining components of a conventional DC/DC converter.
According to a further preferred embodiment, said internal electrical circuit is a baseband digital part and said internal logical control signal is derived from a control logic of said baseband digital part.
According to a further preferred embodiment, said first switching state corresponds to a low output power requirement and said second switching state corresponds to a high output power requirement of said internal electrical circuit.
According to a further preferred embodiment, said internal logical control signal is used to changeover from a first low power low, frequency clock source to a second high power, high frequency clock source for said internal electrical circuit. This signal indicates the changeover between the sleep and traffic modes and is usually generated by an internal counter circuit.